Unfortunately, it seems that a Thunderbird update has caused the problem of losing your email accounts and calendars. But don't worry, you can restore the old profile file to restore your accounts and calendars. Here are the steps that can be followed: Close Thunderbird completely. Find the files folder of your old Thunderbird profile. It is usually stored in a location like: C:\Users\YourUserName\AppData\Roaming\Thunderbird\Profiles\. Find a folder containing files and folders that look like this pattern: random.default. "random" will be a random string of letters and numbers. Copy this entire folder and paste it somewhere convenient on your computer for later use. Now, open the new Thunderbird. Go to Help > Technical Information in the menu bar. In the About App section, click Folders at the bottom of the page. Click "Open Folder" next to "Folder for Files." You will be taken to your new Thunderbird profile folder. Close Thunderbird. Open the opened folder and click on the "Profiles" folder. Move the old folder you copied in step 4 to this folder. Open Thunderbird again, and once it's open, your email accounts and calendars should appear as they were. Please note that this may require some time as Thunderbird may reload and rebuild some data.